What are custom controls?

A control is a reusable component such as a textbox, label, or drop-down list. Many standard controls come built into .NET, and you can inherit from ("extend") these controls to accomplish many useful things.
 

Why would you use one?

• Storage of additional information in a control
  

  It is sometimes useful to create each instance of a control with identifying information. For example, if you have a grid of many buttons where each button, when clicked, calls the same event handler in the form that contains the buttons--and the form then needs the button to tell it which button was clicked. This can be done with a customized button, where you pass the button's identifying information to the button constructor (such as what row and column it's in). When the button is clicked, the form's event handler can ask the button which row and column it's in. The code additions to the button are minimal--pass in a couple of arguments to the constructor, and provide a property (getter and setter) to cough up the passed-in arguments to the form later.

• Addition or modification of standard features
  

  Suppose I want all my buttons to be light blue, but turn yellow when your mouse is over it. Instead of setting these properties individually on each button and have duplicate code in each button handler, I could use a custom control and add this behavior to a specialized "custom button". Then, all the custom buttons would automatically behave this way. As with any control, I could even reuse this custom control in many different projects.

Two ways of using custom controls

1. Use the Windows Forms Designer and the Toolbox to drag custom controls onto a form
   

   This is for visual, manual placement on a form by dragging and resizing. For this case, these are the basic steps: Use the New Project wizard to create a Windows Control Library project. Edit the custom control class to do what you want. Build the project (which compiles to a .dll file). Add the custom control .dll to the Toolbox. Drag the custom control from the Toolbox onto the form.

   
   Please work through Tutorial 1 to try the above.
    
   
2. Add custom controls by writing code (important if there are many identical controls)
   

   This is typically used for the information storage type. If you have to send individual information to each control when it's instantiated, you'll have to write code to do it. For this case, these are the basic steps: Add a UserControl class to your project. Edit the custom control class to do what you want. Write code explicitly to add the custom control to your form.

   
   Please work through Tutorial 2 to try the above.
    
   

Visitors: